If Spirits Are So Smart, Why Do Humans Need Brains?

I personally understand this concept by thinking of it as "density." Earth is a place that is "solid" and "dense" compared to the Other Side. Why do spirits come down for lifetimes to begin with? Well, obviously to grow, but the multiverse is set up so that on the Other Side, spirits never experience pain. Ever. And after going for the equivalent of one hundred or so years without experiencing pain, spirits start to feel weird and crave pain bad. However, there may be a difference in how we think of pain and how spirits think of pain... yes, hurting yourself physically creates pain, but also, it could just be that being "crammed" in a body or experiencing the density of being on Earth, is what spirits consider pain, compared to what they experience on the Other Side. When a spirit is crammed into a body and experiences the awkwardness of being in a human "dense" form, it helps with cognition if they have a brain to think. However, ghosts who are Earthbound are sometimes capable of some sort of intelligence, depending on the intelligence of the soul. Some ghosts may possess some intelligence, while others do not. So, in short, a soul does not need a brain to be intelligent, however humans are much more intelligent than ghosts. I do not understand the way the Other Side is set up, and it seems to be a "don't go there," meaning it is hard to explain to a human on Earth. One time, a spirit who was making a joke about being disgruntled said he had been wandering around, "complaining about other souls touching him." Then he explained, on the Other Side, strangers would never touch you, ever. There is some reason why that could never happen. Spirits have physical forms, or visual forms. They have two eyes, a nose, and a mouth. Typically that's true on all other planes (for lifetimes, besides Earth), as well as on the Other Side. How attractive your physical form is corresponds directly with how attractive your soul is (based on soul traits). God never has to come down for lifetimes. He has ways of experiencing pain without living lifetimes.